The major regulatory enzyme is hepatic cholesterol biosynthesis is 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase or EC 1.1.1.34) which catalyzes the reduction of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) to mevalonic acid. Inhibitors of HMG-CoA reductase inhibit or regulate the biosynthesis of cholesterol in mammals and are valuable agents in the prevention of adverse physiological effects induced by cholesterol.